Much or our discourse around environmental issues involves hazards like air and water pollution, deforestation, species extinction or the looming consequences of global climate change. Rarely do we ponder the importance of protecting the natural environment as a mental health resource. Yet, increasingly, scientists from varied disciplines are investigating how interaction with the natural world can improve both physical and psychological health. For those feeling discouraged about the seemingly overwhelming environmental problems we face and the many barriers to changing destructive behaviour, the notion of nature as a source of health, healing and even happiness is exciting.

A growing body of evidence points to the importance of green space for mitigating the health hazards associated with urbanization, such as heart disease, respiratory illness, low birth weight, poor immune functioning and higher mortality. Several decades of research in Japan, Korea and Finland have demonstrated that natural and urban environments affect the human stress response differently. People immersed in nature show benefits on a variety of physiological indicators, such as heart rate variability, levels of cortisol (the "fight or flight" hormone), the presence of anti-cancer proteins and the natural killer-ceil activity important for immune functioning.

Contact with nature improves mental health as well. People suffering from clinical depression ruminate less and have more positive emotions after walking through an arboretum than after walking in an urban core. Beyond simply reducing stress and ill-being, natural environments can enhance problem solving, concentration and social cohesion. Not surprisingly, in greener communities neighbours interact more with each other and people feel safer and better adjusted.

Even brief contact with unspectacular urbanized nature can increase happiness more than we realize. Researchers who asked people to predict in advance what their mood would be...